1. Field of the Invention
The invention relates generally to gas mask respiratory protection in contaminated environments. More particularly, the invention is directed to an advanced chemical-biological mask for protecting a wearer from chemical and biological environmental contaminants. The mask is especially suitable for military applications, but is of interest in any civil emergency situation where highly toxic substances are in the atmosphere.
2. Description of the Related Art
Since World War I, various nations throughout the world have possessed chemical-biological (CB) agents and delivery systems capable of striking military and civilian targets with little or no warning. To minimize the effects of CB attacks, there is a need for reliable, durable, lightweight, foldable, comfortable, and small-sized protective masks for use by military and civilian populations in emergency situations in contaminated environments. Such a mask should provide the wearer with a leak-proof protection for an extended time period (e.g., twenty-four hours).
For the reasons stated below, conventional chemical-biological masks cannot satisfy the above-noted need due their deficiencies in weight/bulk, fit/comfort, optical compatibility, breathing resistance, communications, and protection.
A. Weight/Bulk
A primary thrust in current U.S. Army plans for the future battlefield is to "Lighten the Soldier's Load", i.e., lessen the soldiers weight carrying burden to increase mobility. Gear such as the protective mask must always be carried during operations (whether it is needed/used or not) since it provides critical life-saving protection and need is unpredictable. However, the Army's current M40 mask is not conducive to the Light Forces concept due to its weight and bulk.
For example, the M40 cannot be easily rolled-up in the carrier and occupies too much space for normal combat operations. It requires a special carrier that must be carried in addition to the soldier's backpack. A reduction in size is needed to allow transport as part of the user's backpack or storage in a pocket.
B. Fit/Comfort
Lack of comfort is a product of several factors in the M40 mask. The suspension system has thick strapping and metal buckles which cause hot spots on the user's head. The combined weight of the mask, hood, and canister on the head causes neck strain. The relatively heavy filter canister bounces when the user moves quickly, causing the mask to jerk the head of the wearer. In addition, the canister causes an uneven weight distribution further aggravating the neck strain. Moreover, people with unusual facial structures do not fall within the three sizes of the M40 mask.
C. Optical Compatibility
Due to the eye relief of the M40 being 45 millimeters, many sighting devices within the Army inventory either cannot be used or the field-of-view is significantly reduced. The eye relief typically required is 25 millimeters. The filter canister, since it is located on the facepiece, also poses compatibility problems with weapon systems.
D. Breathing Resistance
Breathing resistance creates a significant physiological burden for the user of any mask. Overall, the goal of the present invention was to decrease inhalation and exhalation resistances by a factor of two (2) over current military masks, such as the M40, to satisfy physiological goals. There are essentially three methods of reducing breathing resistance for a mask, all of which are utilized in the present invention. Surface area of the filter may be increased, lower resistance filter media may be used, and the resistance of inlet and outlet valves may be reduced. For the present invention, the flapper type valves were redesigned or replaced by lower resistance valves. The C2 canister (which is the filter used with the M40) has a 45 mm of H.sub.2 O resistance when measured at 85 Ipm, which is improved for the present invention with an alternate filter design.
E. Communications
The passive kapton film voicemitter provides an average of 75% word recognition using the standard U.S. Army Modified Rhyme Test. An average of 91% is determined necessary to match recognition without a mask. Any variability or loosening of the film tension results in further performance reductions.
F. Protection
The seal of the M40 provides very good protection under normal conditions but may be subject to leakage under unusual conditions. With head movement, the face mounted canister can cause a torque on the facepiece and subsequent leakage. The rigidity of the facepiece structure can prevent adequate sealing during extreme facial movements.
The existing liquid protection hood system available for military masks only provides for a 6 hour liquid agent resistance as opposed to the desired 24 hours. While the second skin covers the mask and provides the desired 24 hours, it significantly adds to the weight and bulk of the present mask systems.